Recent functional neuroimaging studies in humans and rodents have shown that the anterior cingulate cortex (ACC) is activated by painful stimuli, and plays an important role in the affective aspect of pain sensation. The aim of the present study was to develop a suitable stimulation method for direct activation of the brain in fMRI studies and to investigate the functional connectivity in the thalamo-cingulate pathway. In the first part of the study, tungsten, stainless steel, or glass-coated carbon fiber microelectrodes were implanted in the left medial thalamus (MT) of anesthetized rats, and T 2 *-weighted gradient-echo (GE) images were obtained in the sagittal plane on a 4.7 T system (Biospec BMT 47/40). Only the images obtained with the carbon fiber electrode were acceptable without a reduction of the signal-to-noise ratio (SNR) and image distortion. In the second part of the study, a series of two-slice GE images were acquired during electrical stimulation of the MT with the use of a carbon fiber electrode. A cross-correlation analysis showed that the signal intensities of activated areas in the ipsilateral Functional MRI (fMRI) is a noninvasive imaging technique for mapping brain function that utilizes neuronal activityinduced changes in blood oxygenation. These changes result in a high local concentration of deoxyhemoglobin, the paramagnetic properties of which cause blood oxygen level-dependent (BOLD) contrast (1,2). fMRI provides spatial information about multiple brain activations, and allows the functional assessment of specific sensory pathways; therefore, it is increasingly being used to elucidate the functional organization of the human brain (3). However, current fMRI methods are of limited use in exploring longrange interactions between different brain structures and specific functional activation by known neuroanatomical pathways, which require the invasive implantation of an intracranial stimulation electrode or cannula to electrically or chemically excite specific brain structures.Invasive stimulation of a deep brain region has long been used in patients to alleviate intractable pain (4,5), and a recent study using PET imaging demonstrated that the anterior cingulate cortex (ACC) is activated during thalamic deep brain stimulation in patients with chronic pain (6). However, the use of direct electrical brain stimulation in fMRI studies has potential hazards associated with the direct application of electrical current to brain tissue in the magnetic bore, and thus there is a need for a safe, efficient method for electrical brain stimulation in such studies. Several MR-compatible electrical stimulation methods for use in humans have been developed (7-10), but the strong magnetic field interference elicited by metal electrodes is still a problem in direct electrical brain stimulation in fMRI studies.fMRI studies using animal models allow invasive investigation of the neuronal mechanism underlying the brain activation shown by the BOLD signals (11). Furthermore, studies of the effect of pharmacolo...